1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and the like, a process cartridge mountable within such image forming apparatus, and a method for attaching a photosensitive drum to such process cartridge.
2. Related Background Art
In a conventional process cartridge, as shown in FIG. 32, a photosensitive drum is attached to arm portions 141, 142 extending from a cleaner container 140 via support pins 143, 144. The support pins 143, 144 are fitted into holes formed in gear flanges 146, 147 secured to both ends of the photosensitive drum 145 by adhesive. When the process cartridge is mounted within an image forming apparatus, the gear flange 146 is meshed with a drive gear (not shown) of the image forming apparatus, so that the photosensitive drum 145 can be rotated in a predetermined direction at a predetermined number of revolutions. The support pins 143, 144 are secured in holes formed in the arms 141, 142 of the cleaner container 140 via screws.
However, in the above conventional process cartridge, due to the combination of the play between the holes of the cleaner container 140 and the support pins and the play between the support pins and the holes of the gear flanges, it was feared that a rotary axis of the photosensitive drum was deviated from a designed value or set value. Particularly, when the driving force is transmitted from the drive gear of the image forming apparatus to the flange gear, the photosensitive drum is displaced in a direction inclined by an angle corresponding to a pressure angle regarding a tangential line on base pitch circles of the drive gear and the flange gear, with the result that the light image of an original and the laser beam are incident to the photosensitive drum obliquely with respect to the axial direction of the drum, thereby worsening the perpendicularity of an image.
To avoid this, conventional rolling bearings may be used. However, since such rolling bearings are expensive, it is not desirable to use the roller bearings with a process cartridge having a limited service life.
Alternatively, it is considered that the support pins are completely press-fitted into the holes of the cleaner container. In this case, however, since there arise the problems in manufacturing that the assembling operability is worsened and that the photosensitive drum of a process cartridge which did not pass muster cannot be exchanged, it is difficult to utilize such a press-fit technique practically.
In particular, recently, since the image obtained by the image forming apparatus has been finer and more accurate, and the resolving power of the image is also improved, even a slight deviation and/or vibration of the rotary shaft of the photosensitive drum cause a serious problem.